A 28% Bill Jump at a 120-Room Hotel: Cooling Tower and Landscape
A 120-room hotel's annual water use rose from 11.1 to 14.2 million gallons with no change in occupancy. Water costs $4.10 and sewer $5.10 per 1,000 gallons, billed on 100% of metered volume with no irrigation credit. Interval data show a night-time minimum flow of 6.0 gpm between 1 a.m. and 5 a.m.; the historic minimum was 0.8 gpm.
The property has one master meter and no submeters. The 200-ton cooling tower runs year-round at about two cycles of concentration, with makeup controlled by a float valve that has been adjusted three times; the maintenance log records the basin overflowing to a floor drain as recently as six weeks ago. Landscaping is 1.8 acres of turf and beds on a 14-station automatic controller with no rain sensor and no dedicated irrigation meter; three heads are visibly broken and one zone valve is stuck open. Housekeeping, laundry operations and occupancy (71% in both years) are unchanged.
1. Build the water balance for the 3.1 million gallon increase and locate the loss before recommending any equipment.
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Do the balance first. The gap is 14.2 - 11.1 = 3.1 million gallons, or 8,493 gpd.
- The interval data are decisive: 6.0 gpm at night against a 0.8 gpm baseline means 5.2 gpm of flow while the building sleeps. That is not guests; it is mechanical or irrigation failure. Running continuously: 5.2 x 1,440 = 7,488 gpd = 2.73 million gallons per year.
- The remainder, about 1,000 gpd (0.37 million gallons), matches the stuck zone valve plus three broken heads.
- Cost: 3.1 million x $9.20/1,000 = about $28,500 per year, roughly $25,100 of it the continuous 5.2 gpm.
Diagnosis order: the loss is continuous and independent of occupancy, so isolate it. Close the tower makeup overnight and read the meter; if night flow falls to baseline, the tower is the source. If not, close the irrigation master valve the following night. Two nights of testing cost nothing and will beat a contractor's leak survey for speed.
Judgement: do not start with submetering. Submeters document the problem; they do not fix it, and the meter data already told you the loss is continuous rather than occupancy-driven.
2. What is the likely source of the 5.2 gpm, and how far should the tower cycles of concentration be pushed?
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The overflow is the likely 5.2 gpm. A float valve adjusted three times, with a basin overflowing to a floor drain, sends makeup water straight to sewer at whatever rate the float passes - continuous, day and night, exactly matching the interval signature. Replace the float with a conductivity-controlled solenoid, set the mechanical overflow above normal operating level, and verify the basin holds at the new setpoint.
Then raise cycles of concentration:
- At 2.0 cycles, blowdown equals evaporation; at 4.0 cycles it is one third of evaporation.
- With evaporation of about 2,400 gpd, blowdown falls from about 2,400 to 800 gpd - 1,600 gpd, or 584,000 gallons a year, about $5,370 at $9.20 per 1,000.
- A controller at roughly $7,500 plus chemistry gives about a two-year payback at this rate.
Constraint: do not chase cycles blindly. Hold the LSI near +0.5 to +1.0 with an inhibitor matched to the makeup chemistry, and stop where silica or calcium limits scaling in the fill. Verify the drift eliminators are intact, since drift is water leaving the system without doing any work.
3. What metering and irrigation measures do you recommend, and in what order relative to the repairs?
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Find the loss, fix the loss, then measure permanently.
- Fix what is already known: the tower float, the stuck zone valve, the three broken heads. Nothing downstream matters until those are closed, and the first month of post-repair data becomes the new benchmark.
- Install four submeters - domestic, laundry, cooling tower makeup, irrigation - so the next unexplained change is isolated in a day rather than a year. Give operations a nightly minimum-flow target; anything above about 1 gpm warrants investigation that week.
- Move irrigation to a smart controller with rain shutoff and matched-precipitation nozzles, and put the dedicated irrigation meter on the utility account to capture any sewer abatement. At $5.10 per 1,000 gallons this often pays for the meter in one season - but confirm the abatement with the utility rather than assuming.
- Replace high-water turf with drip-irrigated beds in stages. At 1.8 acres this is a multi-year capital item, so convert by zone and track the metered result rather than claiming an unverified saving.
Reporting: give the owner a one-page water balance - domestic, tower, irrigation - because a hotel cannot manage 14 million gallons a year from a single master meter.